1. Field of the Invention
The present invention relates to a thermoplastic resin composition. More particularly, it pertains to a thermoplastic resin composition which comprises as the principal component a styrenic polymer having a high degree of syndiotactic configuration, said composition being improved in long-term heat resistant stability by being compounded with a polyphenylene ether that is modified by a compound having an ethylenic double bond and a polar group in the same molecule (particularly typified by maleic anhydride) or a derivative thereof at a modification rate of not less than 1.3% by weight (hereinafter sometimes referred to as "Maleic anyhydride-modified PPO" or simply "Modified PPO"), and at the same time, to a process capable of efficiently producing the Maleic anhydride-modified PPO.
2. Description of Related Art
There has heretofore been adopted the technique for improving various thermoplastic resins in the dynamical properties (or mechanical properties), especially rigidity and heat resistance by compounding therein an inorganic filler such as glass fiber. There are proposed the thermoplastic resin compositions excellent in heat resistance and dynamical properties, for example, in Japanese Patent Application Laid-Open Nos. 257948/1987 and 182344/1990 in which syndiotactic polystyrenes are compounded with an inorganic filler, and a thermoplastic resin and/or rubber together with an inorganic filler, respectively. However, the aforesaid technique has been incapable of producing a satisfactory resin composition even if compounded with an inorganic filler because of the insufficient adhesivity between a syndiotactic polystyrene (SPS) and an inorganic filler.
Such being the case, Japanese Patent Application Laid-Open No. 126743/1991 discloses the improved technique over the aforementioned ones in which a syndiotactic polystyrene is incorporated with a maleic anhydride-modified PPO to provide a resin composition excellent in impact resistance, heat resistance and mechanical properties. The aforesaid improved technique, however, necessitates at least 5% by weight of the maleic anhydride-modified PPO to be incorporated therein for the purpose of sufficienty exhibiting the effect owing to its low modification rate.
Nevertheless it has been found, as a result of long-term heat resistance test for the resin composition incorporated with the maleic anhydride-modified PPO, that the decrease in the molecular weight of the syndiotactic polystyrene (SPS) is made remarkable by the increase in the loading of the maleic anhydride-modified PPO causing deterioration of dynamical properties of the composition, and that a loading thereof of 5% by weight or more further accelerate the aforestated unfavorable tendency. Moreover in order to allow an alloy-based resin composition incorporated with polyamide to exert a sufficient compatibility effect, it is necessary to add a large amount of maleic anhydride-modified PPO to the composition, thus lowering the crystallinity of SPS. Likewise, the decrease in the molecular weight of SPS is inevitable in the long-term heat resistance test for the composition.